A typical conventional torque limiter of this type includes an outer annular member, an inner ring received in the outer annular member and rotatably supported by a boss portion provided at one end of the outer annular member, a coil spring having a constant diameter and fitted on the radially outer surface of the inner ring with an interference fit, and a lid member fitted in the radially inner surface of the outer annular member at the other end thereof, thereby closing the gap between the radially inner surface of the outer annular member and the radially outer surface of the inner ring (see JP Patent Publication 2006-170307A).
The coil spring of this torque limiter has its two cut end portions in engagement with the outer annular member and the lid member, respectively, thereby generating required torque when the inner ring and the outer annular member rotate relative to each other and the coil spring is radially expanded.
Since the coil spring comprises a coil having a constant diameter and comprising a steel wire having both ends simply cut perpendicular to the axis of the wire without forming radially bent hooks at both ends of the coil, the entire torque limiter is sufficiently small in size.